It is known in the art to make sheet metal panels at the use site from flat sheet metal, using a roll forming machine. Typically, the panel in its final form will be trough-shaped or generally U-shaped having a base and two vertical sidewalls extending from the sides of the base. One or both sidewalls usually have a lateral flange for joining two panels side by side to form a unitary assembly. Cutting a panel to the desired length has heretofore been accomplished by cutting either immediately prior to beginning the forming operation or immediately after the completion of the forming operation. A disadvantage of either method of cutting the panel is that the additional space required to perform the cutting operation will be approximately as great as that required for the entire forming operation itself. Another disadvantage of cutting the sheet metal prior to the forming operation is that this precludes automatic feeding of the sheet metal into the forming machine from a large roll of sheet metal, thereby wasting time by manually performing a task which could be done automatically. On the other hand, when the panel is cut after completion of the forming operation the vertical sidewalls and their lateral flanges present further problems. Shearing a fully formed panel having vertical sidewalls maximizes the length of the blade stroke required, thereby decreasing efficiency and precision in the cutting operation. In addition, because the sidewalls of a fully formed panel are generally vertical, they are particularly susceptible to crushing and tearing during a shearing process. One way to alleviate this problem has been to cut the formed panels by hand, but this solution is difficult and time consuming.
An additional problem with cutting the panel after the forming operation is that the force of the shearing action typically produces deformities in the panel near the cut. While these deformities may be rolled out during the forming operation if the cutting is performed prior to beginning the final forming, this is not possible if the panel is cut after final forming. In the latter case, such imperfections in the panel must either be accepted as they are or additional steps must be taken to smooth them from the panel.
A further problem with devices for shearing formed panels has been that generally only a single width and configuration of panel may be sheared by the device. This has been primarily due to the fixed dimensions and locations of the cutting support structures for the sidewalls and flanges. For example, U.S. Pat. No. 3,771,401 to Jasinski discloses a sheet metal shearing apparatus which provides a form-fitting structure to fully support all areas of the panel during the cutting operation, thereby protecting against deformation from pressures exerted by the shearing. However, the Jasinski apparatus requires a precise fit between the formed panel and the form-fitting support structure, and such precision may be difficult and time consuming to achieve and to maintain in on-site cutting operations. In addition, the Jasinski device is adapted to support sidewalls and flanges of a particular configuration, and is not suitable for different configurations. Furthermore, the Jasinski device is designed for cutting panels of one particular width, and i not adjustable to provide for cutting of panels over a range of widths.
When shearing sheet metal using a cutting blade which passes through the metal and between a pair of dies on which the metal rests, the stroke of the blade cuts out a narrow strip of metal along the length of the cut. This cut-out strip must pass cleanly between the dies and out of the path of the blade, or the accumulation of the strips between the dies will result in jamming of the cutting action. This problem has been solved in the prior art by undercutting a portion of the dies beginning just below their upper cutting surface, thus effectively widening the channel between the dies and increasing the clearance allowed for the cut out strip to pass through the dies. This solution is illustrated by the Jasinski apparatus, as well as by U.S. Pat. No. 4,218,946 to Witzler. The disadvantage of this approach is that widening the channel between the dies may also adversely affect the precision of the shearing action by allowing the stroke of the blade to deviate from a straight course.